Bearings are typically used in rotating equipment to allow relative motion between two parts. For example, a ball bearing or a roller bearing may be used to allow a shaft to rotate within a fixed housing. A journal bearing is a simple bearing for use with a rotating shaft. In a journal bearing, the “journal” refers to a portion of the shaft and the “bushing” is a hollow cylinder surrounding the journal. The bushing is set into a housing or other casing which may be called the “journal box.”
Typically, both the journal and the bushing are smooth polished cylinders. The gap between the journal and the bushing may be referred to as the “clearance” of the bearing. In a journal bearing, a lubricant is added within the clearance between the journal and the bushing. The lubricant is typically viscous enough to provide a cushion between the rotating journal and the stationary bushing.
FIG. 1 illustrates an example of a prior art system including a rotating device 1. Rotating device 1 may include any sort of rotating equipment (e.g., a motor, a pump, etc.). Rotating device 1 includes a stationary housing 10 with an end cap 12 and a journal box 14. Rotating device 1 also includes a rotating shaft 20 with a rotating element 22 and a journal bearing 24. Rotating element 22 may include any component of rotating device 1 (e.g., a rotor, an impeller, etc.).
FIGS. 2A-2D illustrate various aspects of prior art journal bearing 24. FIG. 2A shows a longitudinal cross-section of a bushing 26 with a bushing interior surface 28. Bushing 26 is a hollow cylinder configured to house a journal 27. FIG. 2B shows journal 27 having a journal exterior surface 29. As shown in FIG. 2C, journal 27 rests inside bushing 26 to form bearing 24.
FIG. 2D shows a cross-section of bearing 24 taken along line 2D-2D shown in FIG. 2C, with arrow 30 showing the direction of rotation of rotating shaft 20 and journal 27. The gap between bushing 26 and journal 27 is a clearance 34. A lubricant 32 is introduced into clearance 34. The rotation of journal 27 within bushing 26 creates a “wedge” of lubricant 32. Journal 27 rests on the wedge of lubricant 32 without coming in direct contact with bushing 26.
In some applications, lubricant 32 is circulated through the interior of rotating device 1 and any bearings 24 to both remove heat and provide lubrication. In normal canned motor applications, the amount of lubricant 32 adequate to cool bearing 24 is smaller than the amount of lubricant 32 needed to cool the motor and/or its components. In those applications, some portion of lubricant 32 bypasses bearing 24 avoiding the pressure drop attendant to passing through clearance 34—there is a high resistance to flow through the clearance 34 of many journal bearings. The design of a close clearance journal bearing is significantly constrained by the balance between the pressure drop of the lubricant and the minimum allowable flow rate. In addition, as the rate of rotation of rotational device 1 increases, so does the resistance to flow through clearance 34. Some journal bearings include one or more grooves in a bearing surface—reducing the resistance to flow through the clearance.